The automotive industry is in a tight spot. Customer demand and the Corporate Average Fuel Economy (CAFE) standards for 2025 are driving a focus on generating an average new vehicle fuel economy of more than 60 miles per gallon for cars and 43 miles per gallon for trucks by 2025. In order to reach this goal, vehicle lightweighting has become a major focus area, with the highest immediate benefits coming from increased use of lightweight materials. A weight reduction of 10 percent corresponds to a 6-7 percent increase in fuel economy. Aluminum is approximately ⅓ lighter than steel and, as such, the switch from steels to lightweight, high strength aluminum alloys is very important. For example, the Honda Accord, the second-bestselling car for its segment in the U.S. (in 2010), is almost 50 percent steel. For example, switching body panels and enclosures to aluminum will reduce the weight by approximately 20 percent, increasing the fuel economy by 12-14 percent.
The problem is that automobile manufacturers are already doing everything they can to reduce vehicle weight. Automotive components are being designed down to the gram, but they are still often too heavy. As a result, manufacturers are forcing aluminum into vehicles despite insufficient manufacturing processes.
In the past, many automotive companies disregarded the benefits of aluminum manufacturing technologies that were incapable of processing parts economically and capturing the full capabilities of the materials. However, customer demand and CAFE standards are forcing aluminum into automotive vehicle designs, which will be costly unless new manufacturing processes are developed. Common manufacturing processes for aluminum and magnesium alloys are warm forming, casting, or thixotropic forming, followed by separate tempering operations.
Warm forming is primarily an aluminum sheet metal process that uses a heated die and blank to enhance formability. While the process is capable of producing typical stamped automotive geometries, the yield strength is too low for many automotive applications.
Casting processes are well known and capable of producing molded parts with stiffening features; however, castable alloys are typically undesirable because of their brittleness and microscopic defects. Furthermore, castings are not suited for large, thin components, such as aluminum sheets, that are common in many automotive applications.
Thixotropic forming is a process that is capable of producing thin, complex geometry, particularly for consumer products. The process, however, has aspect ratio limitations and is prone to microscopic flaws like dispersion issues and grain boundary problems, so there are not many applications for aluminum alloys. Like warm forming, thixotropic forming is not used in many automotive applications because of low yield strength.